Posted on 2006-12-28 19:26
路易 閱讀(215)
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Hibernate
一般網站在處理用戶上傳圖片時通常采用兩種策略：一是直接把圖片存入數據庫中的Blob字段；二是數據庫中只存儲圖片的在服務器上的路徑信息?，圖片存放在分門別類的文件中，使用的時候從數據庫讀取路徑信息到頁面img元素即可．在此不討論兩種方案的優劣，我只是寫了個hibernate的例子來實現第一種策略．例子很簡單，t_user表主要兩個字段，name和photo，其中photo字段類型為Blob．在此例中數據庫我采用mysql，oracle的Blob字段比較特殊，你必須自定義類型，具體的請自行搜索，這方面的資料很多．
//User.java
package?com.denny_blue.hibernate;
import?java.io.Serializable;
import?java.sql.Blob;
public?class?User?implements?Serializable{
?private?Integer?id;
?private?String?name;
?private?Blob?photo;
?/**
??*?@return?the?id
??*/
?public?User(){
?}
?public?Integer?getId()?{
??return?id;
?}
?/**
??*?@param?id?the?id?to?set
??*/
?public?void?setId(Integer?id)?{
??this.id?=?id;
?}
?/**
??*?@return?the?name
??*/
?public?String?getName()?{
??return?name;
?}
?/**
??*?@param?name?the?name?to?set
??*/
?public?void?setName(String?name)?{
??this.name?=?name;
?}
?/**
??*?@return?the?photo
??*/
?public?Blob?getPhoto()?{
??return?photo;
?}
?/**
??*?@param?photo?the?photo?to?set
??*/
?public?void?setPhoto(Blob?photo)?{
??this.photo?=?photo;
?}
?
}
類User有３個屬性，id,name,photo，相應的getter和setter方法以及一個無參構造函數．應該注意的是photo的類型java.sql.Blob
相應的user.hbm.xml應該如下：
<?xml?version="1.0"?>
<!DOCTYPE?hibernate-mapping?PUBLIC
?"-//Hibernate/Hibernate?Mapping?DTD?3.0//EN"
?"
http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd
">
<hibernate-mapping
?package="com.denny_blue.hibernate">
?<class?name="com.denny_blue.hibernate.User"
????????table="t_user"
????????dynamic-update="true"
????????dynamic-insert="true"
????????batch-size="3">
??<id?name="id"
??????column="id"
??????type="java.lang.Integer">
???<generator?class="native"/>
??</id>
??<property?name="name"?column="name"?type="java.lang.String"?lazy="true"/>
??<property?name="photo"?column="photo"?type="java.sql.Blob"/>
?</class>
</hibernate-mapping>
對應的hibernate.cfg.xml配置文件，不再列出，請參照hibernate文檔自行設定．
ＯＫ，做了這一步，我們寫個測試類來進行單元測試：
package?com.denny_blue.test;
import?java.io.FileInputStream;
import?java.io.FileNotFoundException;
import?java.io.FileOutputStream;
import?java.io.IOException;
import?java.io.InputStream;
import?java.sql.Blob;
import?org.hibernate.Hibernate;
import?org.hibernate.HibernateException;
import?org.hibernate.Session;
import?org.hibernate.SessionFactory;
import?org.hibernate.Transaction;
import?org.hibernate.cfg.Configuration;
import?com.denny_blue.hibernate.User;
import?junit.framework.TestCase;
public?class?HibernateTest?extends?TestCase?{
????????private?Session?session;
?protected?void?setUp()?throws?Exception?{
??try{
???Configuration?config=new?Configuration().configure();
???SessionFactory?sf=config.buildSessionFactory();
???session=sf.openSession();
??}catch(HibernateException?e){
???e.printStackTrace();
??}
?}
?protected?void?tearDown()?throws?Exception?{
??try{
???session.close();
??}catch(HibernateException?e){
???e.printStackTrace();
??}
?}
?
?public?void?testSave()throws?FileNotFoundException,IOException{
??User?user=new?User();
??user.setName("jordan");
??FileInputStream?in=new?FileInputStream("C:\\test.gif");
??Blob?photo=Hibernate.createBlob(in);
??user.setPhoto(photo);
??Transaction?tx=null;
??try{
??tx=session.beginTransaction();
??session.saveOrUpdate(user);
??tx.commit();
??}catch(HibernateException?e){
???if(tx!=null)
????tx.rollback();
???e.printStackTrace();
??}finally{
???in.close();
??}
?}
?public?void?testLoad()throws?Exception{
??try{
???User?user=(User)session.load(User.class,?new?Integer(1));
???Blob?photo=user.getPhoto();
???InputStream?in=photo.getBinaryStream();
???FileOutputStream?out=new?FileOutputStream("C:\\out\\test2.gif");
???byte?[]?buf=new?byte[1024];
???int?len;
???while((len=in.read(buf))!=-1){
????out.write(buf,?0,?len);
???}
???in.close();
???out.close();
??}catch(HibernateException?e){
???e.printStackTrace();
??}
?}
}
我們讀取C盤目錄下的test.gif并存儲到數據庫中，然后再取出來寫入C:\out目錄，此時你可以查看下數據表中photo顯示為blob,表示已經成功存入．值的注意的代碼片段就是：
FileInputStream?in=new?FileInputStream("C:\\test.gif");
??Blob?photo=Hibernate.createBlob(in);
我們這里是從磁盤中讀取圖片，實際應用中你可以利用上傳組件得到圖片的２進制數據流，并利用Hibernate.createBlob方法來構造相應的Blob對象．而取圖片則使用
InputStream?in=photo.getBinaryStream();
這只是個簡單的測試類，如果我想從數據庫中取出圖片并現實在頁面上該如何做呢？其實也很簡單，我們先要寫一個servlet，在它的service方法中取出圖片，并＂畫＂到指定頁面上．
package?com.easyjf.asp.action;
import?java.io.InputStream;
import?java.io.OutputStream;
import?java.sql.Blob;
import?javax.servlet.ServletException;
import?javax.servlet.http.HttpServlet;
import?javax.servlet.http.HttpServletRequest;
import?javax.servlet.http.HttpServletResponse;
import?org.hibernate.HibernateException;
import?org.hibernate.Session;
import?org.hibernate.SessionFactory;
import?org.hibernate.cfg.Configuration;
import?com.denny)blue.hibernate.User;
public?class?Test?extends?HttpServlet?{
?/**
??*?Destruction?of?the?servlet.?<br>
??*/
?private?Session?session;
?public?void?destroy()?{
??try{
???session.close();
??}catch(HibernateException?e){
???e.printStackTrace();
??}
?}
?/**
??*?Initialization?of?the?servlet.?<br>
??*
??*?@throws?ServletException?if?an?error?occure
??*/
?public?void?init()?throws?ServletException?{
??try{
???Configuration?config=new?Configuration().configure();
???SessionFactory?sf=config.buildSessionFactory();
???session=sf.openSession();
??}catch(HibernateException?e){
???e.printStackTrace();
??}
?}
????public?void?doGet(HttpServletRequest?request,HttpServletResponse?response)
????{
?????try{
???User?user=(User)session.load(User.class,?new?Integer(1));
???Blob?photo=user.getPhoto();
???InputStream?in=photo.getBinaryStream();
???OutputStream?out=response.getOutputStream();
???byte?[]?buf=new?byte[1024];
???int?len;
???while((len=in.read(buf))!=-1){
????out.write(buf,?0,?len);
???}
???in.close();
???out.close();
??}catch(Exception?e){
???e.printStackTrace();
??}
????}
}
通過response.getOutputStream取得輸出流，其他就與上段代碼一致．servlet寫好了，怎么在頁面調用呢？那就更簡單啦，直接在頁面的img標簽的src屬性上調用該servlet即可，如：
<img?id="test"?src="/servlet/Test"/>